Double wall package for storing items in bacteria-free condition

ABSTRACT

A package is disclosed comprising a double wall, plastic bag having an access opening covered by a readily removable closure membrane bonded to the bag by heat seals adjacent the access opening. Both the bag and the membrane are essentially completely impermeable to bacteria, but the membrane is highly permeable to sterilizing vapor in comparison to the plastic bag. The bag comprises inner and outer plies, portions of which define the access opening, and other portions of which overlap within the confines of the access opening. Along any transverse section of the bag, the combined thickness of the inner and outer plies is essentially the same, thereby facilitating the fabrication of the bag out of high temperature plastic, such as polypropylene, which can withstand steam sterilization temperatures.

United States Patent [191 Schuster [451 Sept. 25, 1973 [76] Inventor: Samuel J. Schuster, 1099 Hillside St., Monterey Park, Calif. 91754 [22] Filed: Mar. 20, 1972 [21] Appl. No.: 236,409

[52] US. CL]. 229/62, 206/632 R, 229/66 [51] Int. Cl 865d 33/16 [58] Field of Search 229/62, 66, 62.5;

Primary ExaminerSarnuel B. Rothberg Assistant ExaminerStephen P. G-arbe Attorney-Robert H. Fraser et al.

[57] ABSTRACT A package is disclosed comprising a double wall, plastic bag having an access opening covered by a readily removable closure membrane bonded to the bag by heat seals adjacent the access opening. Both the bag and the membrane are essentially completely impermeable to bacteria, but the membrane is highly permeable to sterilizing vapor in comparison to the plastic bag. The bag comprises inner and outer plies, portions of which define the access opening, and other portions of which overlap within the confines of the access opening. Along any transverse section of the bag, the combined thickness of the inner and outer plies is essentially the same, thereby facilitating the fabrication of the bag out of high temperature plastic, such as polypropylene, which can withstand steam sterilization temperatures.

29 Claims, 7 Drawing; Figures PATENTED SEP25 I975 SHEET 2 0F 2 DOUBLE WALL PACKAGE FOR STORING ITEMS IN BACTERIA-FREE CONDITION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to packages for storing articles in bacteria-free condition, and particularly to packages which permit sterilization of the stored particles by a variety of sterilizing vapors, provide storage for such articles in bacteria-free condition over extended periods of time and are easily opened to permit ready utilization of the bacteria-free articles.

2. Description of the Prior Art U. S. Pat. No. 3,472,369 issued to the present inventor on Oct. 14, 1969 discloses a package so constructed that the interior of the package and its contents may be readily sterilized by a sterilizing agent such as ethylene oxide. The package of the referenced patent comprises a flexible plastic container or bag having an access opening covered by a removably-attached closure membrane such as a paper tear strip. Although both the plastic bag and closure membrane are essentially completely impermeable to bacteria, and under normal conditions will not allow entry of bacteria, the closure membrane is highly permeable to the sterizing agent in comparison to the plastic bag. The package is fabricated with an open end for receiving the article to be stored. The article is inserted in the package, the open end is sealed with a transverse heat seal and the interior of the package and article are completely sterilized by sterilizing gas which readily enters the package through the closure membrane. The sterilizing gas is withdrawn through the membrane, the article remaining in sterile condition until ready for use. Retrieval of the sterilized article is accomplished by pulling back or completely removing the closure membrane thereby at least partially exposing the access opening through which the article is removed.

The package of the referenced patent which is particularly useful for the storage of disposable articles, meets a combination of essential requirements which have never before been fulfilled in a single product. Thus, the package retains its contents in sterile condition until use (which may take place several months or even more than a year after sterilization), it is low in cost compared to the total cost of the package and contents, the contents are readily visible and, lastly, the package is easily opened while providing sufficient strength to guard against accidental puncture or tearing during handling.

The above-described package is readily manufactured on what is basically a conventional plastic bagmaking machine modified in certain substantial respects to accommodate the fabrication of thepackages described. Briefly, plastic sheet stock is fed in successive steps and folded along spaced, parallel longitudinal fold lines, the side edges of the sheet thereby being brought together either in abutting or overlapping relation to define a longitudinal access opening. The closure membrane, typically in the form of a paper strip, may be fed concurrently along the longitudinal access opening and into contact with the sheet. The paper strip and the sheet are joined by longitudinal heat seals applied along both sides of the'access opening in timed relation with the intermittent feed of the plastic sheet and paper strip. The result is a continuous, flattened, composite tube. A transverse heat sealis then applied at intervals across the width of the composite tube to define individual packages which are then separated from each other adjacent the transverse seal by mechanical or thermal cutting means. Packages with one open end ready to receive the article to be stored are thus provided.

The overlapping configuration of the longitudinal side edge portions defining the access opening has certain advantages most important of which is that it helps preclude entry of foreign matter into the interior of the package when the closure membrane is removed. For example, when the closure membrane is in the form of a paper strip, minute paper fibers may be dislodged upon removal of the strip and these fibers can more easily enter the package in the absence of the overlap described. Moreover, the overlap prevents contact between the closure membrane and the article inside.

On the other hand, the use of the overlap presents certain problems. Thus, when the package is viewed in transverse section differential thicknesses along the section will be observed. The degree of differential thickness may be exemplified as follows: if the plastic sheet and the closure membrane each have a thickness of 4 mils (1 mil equals 0.001 inch) then at the overlap the total thickness of the package material is 16 mils. In contrast, the portions of the package adjacent the overlap but within the confines of the closure membrane have a thickness of 12 mils and still further, the regions of the package on eithr side of the closure membrane are only 8 mils thick. Since heat sealing temperatures increase with material thickness, in order to insure an effective transverse heat seal with a conventional bar-type heat sealer a relatively high sealing temperature is required at the overlap. Such highsealing temperatures, however, sometimes cause burnthroughs in other portions of the package where the thickness is less. Singeing or burning of the closure membrane may also result thereby weakening or perforating the membrane at the affected points. Control of burn-throughs has been found to be extremely critical and difficult to maintain in the context of high production, especially when plastics requiring higher sealing temperatures such as polypropylene, saran, nylon,

or the like, are used.

One solution to the foregoing problem is to utilize a differentially heated transverse bar sealer having higher temperatures along those portions engaging the thicker sections. This is not an altogether reliable technique however. Among other requirements, nearly perfect registration must be maintained atall times between the differentially-heated portions of the heat sealer bar and the corresponding regions of the bags being processed. Thus, to the extent that requirements of commercially feasible production dictate, this is not currently a practical solution.

The package structure of the prior patent, which may be fabricated of essentially any flexible, heat-scalable plastic sheet impermeable to bacteria, including polyethylene, polypropylene, cellophane, nylon, polybutylene, or the like, is especially adapted for sterilization of low temperature sterilizing processes such as the ethylene oxide process which is carried out at about F. Many hospitals and other facilities, however, employ the autoclaving process by which sterilization is accomplished in an air-tight chamber filled with pressurized steam at a temperature well in excess of 212 F. The temperature at which autoclaving or steam sterilization is carried out does not adversely affect the higher temperature plastics such as medium to high density polyethylene, polybutylene, polypropylene, nylon, and the like, but is much too high for low density polyethylene which rapidly melts, shrivels or distorts in the autoclaving environment. Thus, packages of polypropylene or other plastics or plastic compositions which can withstand steam sterilization temperatures have the advantage of being sterilizable by a variety of sterilizing vapors, including ethylene oxide and steam, thereby greatly extending the usefulness and versatility of such packages.

Plastics that can withstand steam sterilization temperatures, however, do not have the excellent heat sealing properties of low density polyethylene the sealing temperatures for a given thickness must be higher and better regulated to produce satisfactory seals on a repetitive, production line basis. Thus, where there is an overlap of sheet material formed of such plastic, the temperature required (especially if the plastic sheet is relatively thick) is sufficient to singe or burn the closure membrane and the thinner plastic sections.

In summary then, those materials, such as polypropylene, that can withstand steam sterilization temperatures also require higher, more carefully regulated sealing temperatures and if a relatively thick sheet of polypropylene is shaped into the overlapping configuration described in the aforementioned patent, the temperatures required are so high that the closure material, typically paper, will be burned. Thus, what is a difficult problem to overcome with ordinary package configurations becomes even more difficult with the higher temperature materials.

SUMMARY OF THE INVENTION The present invention makes possible the utilization of the desirable overlapping arrangement within the confines of the access-opening yet enables use of heat scalable plastics sucy as polypropylene, nylon and polybutylene that can withstand steam sterilization temperatures.

The package of the present inveniton includes a double wall, that is, a two-ply flexible plastic bag. Each ply may be relatively thin (for example, 2 mils); in any event, the combined thickness of both plies is at least sufficient to render the bag structure essentially impermeable to bacteria. The plies of the double wall conjointly define an access opening closed by a closure membrane heat sealed'to the bag about the access opening in a manner facilitating manual removal thereof. The closure membrane, like the bag to which it is attached, is essentially completely impermeable to bacteria but, in contrast to the bag material, is highly permeable to sterilizing vapors such as ethylene oxide, steam, or the like. The package is closed at one end along a transverse heat seal joinder line.

According to a significant aspect of the present invention, the combined thickness of the plies forming the double wall bag is uniform along all transverse sections of the bag. Thus, if each ply is constructed of sheet stock 2 mils thick, the combined thickness of the plies at substantially any point along any transverse section is 8 mils. The only differential thickness along transverse sections of the overall package is due to the presence of the closure membrane. However, this falls within the magnitude of differential thickness which has been found to be tolerable and does not materially influence the effectiveness of, or the ability to apply, the transverse end seals. As a result of the thinness of the individual wall plies in combination with the uniformity of the total cross-sectional thickness of the bag, less critical, substantially lower-sealing temperatures may be utilized thus precluding uneven seals, burnthroughs, singeing, or like damage to the bag and/or closure membrane. The use of polypropylene and other higher temperature plastics thus becomes commercially practical and makes possible sterilization by virtually any presently used sterilizing process.

In accordance with one specific, illustrative embodiment of the invention, the bag includes an inner ply and an outer ply having longitudinal edge portions defining a longitudinally-extending access opening. These edge portions are disposed beneath the closure membrane within the confines of the heat seals joining the closure membrane to the bag. The longitudinal edges of the inner ply lie a short distance inwardly of the longitudinal heat seals to define the access opening; the outer ply, in contrast, hasoverlapping longitudinal portions beneath the closure membrane, the extent of overlap and the length of the overlapping portions being such that the edges of these portions are contiguous or in alignment with the edges of the inner ply. In this fashion, a typical transverse section of the container will have a uniform thickness along virtually the entire width of the container.

A number of alternative arrangements may be employed. For example, the outer ply may be provided with the pverlapping portions instead of the inner ply; or, each of the outer and inner plies may be provided with portions which overlap. Still other combinations are possible and some of these will be covered more fully in the detailed descriptionbelow.

The foregoing structure lends itself exceedingly well I to large scale, low cost production on conventional packaging machinery modified in certain material respects to provide consistently high quality packages.

The article to be sterilized may be inserted manually or by machine, either as a completely separate, subsequent'operation or as a secondary operation on a machine capable-of both forming and filling the package. The package is thereafter completely sealed and subsequently the contents may be completely sterilized by a sterilizing vapor, such as ethylene oxide, steam, or the like, in accordance with well-established techniques.

According to another aspect of the invention, the facesof the two plastic plies forming the bag portion of the package may be cohered mechanically, such as by embossing or rolling the two sheets together under slightly elevated heat and pressure. Cohesion can be increased by treating the contacting surfaces with a corona discharge. Trapped air between the plies is thus avoided and the production of the package is facilitated because the plies cannot move laterally relative to each other during processing by the bag-making machine. The elimination of air between the plies is important if the package is subjected to a rapid, sterilant-purging vacuum cycle as part of the sterilization process. Any pair at atmospheric pressure trapped between the plies will expand during such vacuum cycle and possibly rupture the bag.

Other features of packages in accordance with the invention include the use of different, although compatible plastics, transparencies, and/or thicknesses for the inner and outer plies to achieve specific objectives for given applications.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and features of the invention will be understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. I is a partially broken away perspective view of a package for sterilized items in accordance with the invention;

FIG. 2 is an enlarged, transverse section of the package of FIG; 1, taken along the plane 2-2, and showing details of the package structure;

FIG. 2A is a portion of an enlarged, transverse section, such as shown in FIG. 2, of an alternative embodiment of the package according to the invention;

FIG. 2B is a portion of an enlarged, transverse section, such as shown in FIG. 2, of another .altemative embodiment of a package according to the invention;

FIG. 2C is an enlarged transverse section, such as shown in FIG. 2, of still another alternative embodiment of the package according to the invention;

FIG. 3 is a perspective view of the package of FIG. 1 showing the package during opening with the closure membrane partly removed; and,

FIG. 4 is a perspective view of anotherpackage configuration according to the invention.

DETAILED DESCRIPTION OF THE INVENTION It is to be noted that in the accompanying drawings the thicknesses of the plastic sheets forming the bags and that of the closure membranes have all been greatly exaggerated in order to clearly show their interrelationship. Further, it will be evident that a great many combinations of materials, overall package dimensions, material properties, specific package configurations, and so forth, fall within the purview of the claimed invention. Only relatively few specific examples are shown and discussed herein'and these should not be construed as exhaustive.

For purposes of illustrating the background of the invention and the state of the art, the above-mentioned U. S. Pat. No. 3,472,369 issued to 'the present inventor on Oct. 14, 1969 is incorporated herein by reference.

Referring now to FIGS. 1 and 2, packages in accordance with the present invention may be utilized for the ready sterilization, storage in sterile condition and easy removal of an article 10. From a practical standpoint, there is no limit to the kinds of articles that can besterilized and stored in packages of the invention; such articles may typically include surgical and medical instruments, surgical gloves, garments and related wearing apparel, pipettes, petri dishes, syringes, swabs scalpel blades and food items. The dimensions of the package can be tailored to accommodate the particular article to be sterilized and stored. The disclosed packages are especially suitable where the article is of a low cost, disposable nature but all of the advantages of the invention may be realized regardless of the specific character of the article to be sterilized and stored in sterile condition for subsequent use.

Packages such as that shown in FIG. 1 and 2 mainly comprise a plastic container or bag 12 and a closure membrane 14. The bag 12 is a double wall structure comprising two plies, an outer ply 16 and an inner ply 18. Materials which may be used for the plies 16 and 18 include polyethylene, polypropylene, mixtures of polyethylene and polypropylene, nylon, polybutylene and other heat sealable materials.

In comparison to the closure membrane 14, which will be described more fully later, the combination of the material and the thickness of each ply l6 and 18 is such that the ply exhibits very little permeability to sterilizing vapors such as steam, ethylene oxide, or the like. The extent of impermeability of the plastic to sterilizing vapor is approximately a linear function of thickness, that is, increasing thickness increases the impermeability proportionately in linear fashion. Since.

heavier gauges, for example, 2-4 mils, are typically.

necessary to protect the enclosed article from damage; permeability of the plastic to the sterilizing vapor is'reduced very substantially. Plies thinner than 2 mils, for example, 1.5 mils, may be used where strength is a less important factor.

For most applications, both plies 16 and 18 will be transparent to facilitate inspection and identification of the contents of the package but it will be appreciated that either one or both of the plies 16 and 18 may, be translucent, opaque or tinted. Tinting may be desirable in certain instances to control the entry of electromagnetic radiation in both the visible and non-visible portions of the spectrum.

Each ply 16 and 18 is fabricated from a single continuous sheet of material, the parallel, longitudinal side edges of which are folded inwardly along spaced, parallel longitudinal fold lines. Thus, the outer ply 16 has longitudinal edges 20 and 22 and is folded aboutthe longitudinal foldlines 24. Similarly, the inner 'ply 18 has longitudinal edges 26 and 28 and is folded about the longitudinal fold lines 30. The parallel edges 26 and 28 are spaced transversely to define a longitudinal access opening 32. The access opening 32 is approximately symmetrical of the longitudinal center line 33 of the container 12 but it will be appreciated that the opening can be displaced to one side or the other of the center line. FIG. 4, discussed further below, depicts an example of such an asymmetrical arrangement.

In the embodiment of FIGS. 1 and 2, the outer ply 16 is provided with overlapping portions34 and 36 closing the access opening 32. The extent of overlap of the portions 34 and 36 is such that theedges 22 and 28 are in abutting relationship, or very close to such relationship. The longitudinal edge 20 of the outer ply 16 and the edge 26 of the inner ply 18 are nearly in alignment, that is, they lie approximately in a common vertical plane, the transverse spacing separating; these edges being only that necessary to permit the passage of the portion of the outer ply 16 leading to the overlapping portion 36. By inspection of the transverse section of FIG. 2, it will be seen that along virtually the entire extent of the section, the total thickness of the bag is the same, essentially all portions thereof comprising four layers.

The closure membrane 14 comprises a longitudinal strip somewhat wider than the access opening 32 and its functions are to close the access opening and form a barrier for bacteria while simultaneously being highly permeable to the sterilizing vapor in comparison to the container 12. The closure membrane 14 may be made of conventional paper 3 to 7 mils thick. Paper is characterized by several important properties for purposes of this invention. Unlike plastic, increasing the thickness of paper does not substantially affect its permeability to sterilizing vapors. On the other hand, the labyrinth structure of the fibers constituting paper is such that even modest increases in the thickness of the paper greatly increases its impermeability to bacteria. A long fiber paper, having superior wet strength, should be used where the package is to be subjected to a steam sterilization process.

The paper strip can be provided with a thin polyethylene coating (not shown), such coating being in contact with the outer ply 16. The thickness of the polyethylene coating would preferably be of the order of k mil which is insufiicient to impede the passage of sterilizing vapor but nevertheless would provide a sufficient thickness to facilitate the joinder between the paper strip 14 and the bag 12. Alternatively, direct heat sealing of the paper and the outer ply 16 is made possibly by treating the seal areas-of the plastic with a corona discharge produced by a voltage source of 10-30 kv at a frequency of 3-5 kHz.

Many kinds of paper provide'for an inexpensive, easily handled closure membrane 14 but depending upon particular needs, other materials, both woven and nonwoven, that are impermeable to bacteria yet are comparatively highly permeable to sterilizing vapors may be used. These alternatives would include various paperlike materials such as glass fiber products and Tyvac (a spun polyolefin of the Du Pont Company) which are impermeable to bacteria but, in comparison to the plastic bag 12, highly permeable to sterilizing vaor. p As best seen in FIG. 2, the closure membrane 14 and the plies 16 and 18 are all bonded together along longitudinal joinder lines 40 and 42 symmetrical of the center line 33 and spaced apart somewhat more than the transverse spacing between the edges 26 and 28 of inner ply 18. The bonds are preferably and most easily obtained by heat sealing, using spaced apart heat sealer bars elevated to the required heat sealing temperautre.

The bonding may also be provided by adhesive or other forms of chemical or mechanical bonding.

As shown in HO. 1, the longitudinal joinder lines 40 and 42 may be terminated short of one end of the closure membrane 14 thereby defining a pull tab 44 to provide a manual gripping edge and thereby facilitate removal of the closure membrane 14. The closure membrane 14 may also have transverse extensions 46 and 48 beyond the longitudinal joinder lines 40 and 42 of sufficient width to provide a lateral pull tab on each side of membrane 14 in addition to, or instead of, the end pull tab 44. It is generally sufficient to provide a pull tab of only so much width that it can be grasped with the tips of the fingers. Where greater tearing forces are involved more area may be provided for more secure gripping.

In accordance with one practical example of the invention, the width of the closure membrane 14 is 2% inches in comparison to the overall width of the package of about 6% inches. Thus, the width of the closure memebrane 14 is little more than is of the entire package width and in most instances this is sufficiently narrow to facilitate a view of the article 10 through either face of a package fabricated of transparent plies. The transverse distance between the longitudinal joinder lines 40 and 42 is about 2% inches and the edges 26 and 28 of the inner ply 18 each extend inwardly approximately it inch from the adjacent longitudinal joinder line. Each ply of the container is 2 mils thick and made of transparent polypropylene and the closure membrane 14 is uncoated paper having a thickness of 4 mils. Obviously, great variations in the dimensions, configuration and other characteristics of the package can be made within the purview of the invention.

Referring again to FIG. 1, the transverse end edges 52 and 54 of the plies 16 and 18 respectively, are joined to each other and to the closure membrane 14 by tmasverse joinder lines 56 and 58 each of which is adjacent one of the ends of the package. The joinder lines 56 and 58 are also preferably and most conveniently produced by heat seals. Thus, it will be apparent from FIG. 1 that the longitudinal access opening 32 is completely bounded by a continuous bond or heat seal which is completely impervious to the passage of bacteria.

The closure membrane 14 may include appropriate printed matter, identifying the article 10 contained in the package, the name of the supplier, and so forth. It may alsohave marginal indicia showing the points at which the closure membrane 14 may be most readily gripped for removal and the preferred direction of removal.

If the article 10 is to be inserted manually, the packages may be fabricated individually on a suitable package-making apparatus in which plastic sheet stock is fed intermittently in successive steps, heat sealed across one end and cut into separate packages, the end opposite the heat sealed end being open to receive the article to be sterilized and stored. Standard packaging machines, such as the Simplex manufactured by FMC Corporation, San Jose, California, may be used but require certain modifications the nature of which are unimportant to the disclosure of the present invention but which allow production of the packages of the present invention at an extremely high rate with a great deal of reliability, accuracy, and repeatability.

Generally, the plies 16 and 18 are fed as individual, overlapping sheets from independent supplies, folded over as explained and joined to the closure membrane 14 to form a composite tube stock. The closure membrane 14 is fed concurrently with the plastic sheet stock and is fed along the longitudinal access opening and into contact with the folded outer ply 16. The longitudinal joinder lines 40 and 42 are added by a heat seal mechanism using longitudinal, parallel spaced heater bars and actuated intermittently in timed relation with the feeding of the plastic stock and closure membrane strip. An insulated separator plate is positioned along the path of the composite tube stock within the tube to serve as a backup member for the heat seal elements. Appropriate masking arrangements can be provided in connection with the longitudinal heat sealingoperation to prevent heat seals 40 and 42 from extending all the way to the end of the closure membrane 14 so as to provide the pull tab 44.

After the composite tube stock is formed, the transverse heat sealing and cutting operations may take place in conventional fashion using, for example, either roller elements or heat seal bars to apply the transverse heat seal and either a mechanical or thermal cutter to separate the tube stock adjacent the transverse heat seal.

In the event the package is filled manually, it is fabricated with one open end, as explained, and the article 10 is inserted through the open end which is thereafter sealed with a transverse heat seal. If automatic assembly is used in a combined form and fill operation, the

article 10 is inserted by machine as a secondary operation to the formation of the composite tube as described above. In either case a fully sealed package is provided on a substantially continuous basis.

Certain additional details of the package according to the present invention should particularly be noted. The package is substantially rectangular when empty but is extremely flexible so that it conforms appropriately to the inserted article 10. The inner and outer plies 16 and 18 have sufficient strength to provide adequate protection equivalent to conventional packaging. The plies 16 and 18, when not cohered, are further free to slide relative to one another to greatly increase the resistance of the package to damage by abrading. The tear strength of the closure membrane 14 relative to the strength of the longitudinal joinder lines 40 and 42 is such that the closure membrane 14 is separable from the rest of the package in one piece so that the production of paper particles and fibers during the removal process is minimized. In any event, the overlapping construction of the outer ply l6 impedes the entry into the interior of the package of any foreign matter such as dislodged paper particles and fibers.

After loading and complete closure of the package, the entire interior of the package along with the article 10 are sterilized by steam, or by processes involving the use of sterilizing gases such as ethylene oxide. These operations in any event are simple and inexpensive. For example, containment of the package within an ethylene oxide atmosphere for a short period such as a few minutes is sufficient for the gas to completely fill the interior of the package and allow the gas to contact and sterilize all accessible surfaces within the accepted sterilization times. Thereafter, the placement of the package, in an enclosed chamber held at or near vacuum levels for another short interval, for example, a few minutes, is adequate to purge the package of ethylene oxide. The package isthen ready for storage and use. Autoclaving or steam sterilization is similar except that the process is carried out with steam as the sterilant at a substantially higher temperature.

To use the package the closure membrane 14 is grasped by the pull tab 44 and pulled back, as shown in FIG. 3. Upon complete removal of the membrane 14, the article 10 is readily removed from the package.

Any air that might otherwise become trapped within the space between the plies can be removed by cohering the plies, that is, by intimately uniting the faces of the sheet stack mechanically. Mechanical cohering may be accomplished by rolling under slightly elevated temperature and pressure or embossing the plies together; such treatment has the further advantage of facilitating separation of the overlapping portions of the plies within the confines of the access opening. Embossing techniques and patterns which will accomplish the desired results are well known in the art. Elimination of air between the plies precludes rupture of the bag during the sterilant-purging vacuum cycle and permits such cycle to be rapidly applied to decrease the overall residence time of the bag in the sterilizing apparatus. The cohesion between the sheet stock forming the plies of the bag can be enhanced by pretreating the contacting surfaces with a corona discharge pursuant to practices well known in the art.

The uniformity of the transverse cross-section of the container 12 essentially eliminates burn-through and other problems related to excessive differential thicknesses. The overlayof the closure membrane 14 does result in a greater thickness differential (which adds 3 to 7 mils to the overall or total thickness) but can be tolerated without any adverse results. Thus, production rates are greatly increased and the rejection rate is minimized. Neither precisely controlled heat seal bar temperatures nor differentially heated bars are required.

A number of alternatives will suggest themselves to those skilled in the art. For example, the longitudinal joinder lines 40 and 42 may not only be provided by different types of bonds but may have different strengths so that removal of the closure membrane might be from one side only. Similarly, a gripping edge need be provided only on one side of theaccess opening 32. For many applications other sealing techniques can be used such as radio frequency (RF) sealing.

Turning now to FIG. 2A, an alternative overlap arrangement is illustrated. The package of this embodiment includes outer and inner plies 64 and66, respectively. In this embodiment, the inner ply 66 (as opposed to the outer ply 16 in the embodiment of FIGS. land 2), is provided with longitudinal overlapping portions 68 and 70, the longitudinal edges 72 and 74 of the outer ply 64 disposed a short distance inwardly of the longitudinal joinder lines 76 and 78 to define the access opening. All of the features and alternatives discussed in connection with the embodimentof FIGS. 1 and 2 pertain to the package configuration of FIG. 2A, the only differences being that the longitudinal extremities of the access opening are defined by the outer ply64 and the inner ply 66 is provided with the overlapping portions.

. In FIG. 23, another alternative is shown in which the outer ply 84 has a portion 86 overlapping with a portion 90 of the inner ply 88. Thus, the longitudinal edges 92 and 94 of the outer ply 84 are in abutting or closely spaced relationship along a longitudinal line lying on one side of the package center line andadjacent one of the longitudinal joinder lines 96 and 98. The longitudinal edges 100 and 102 of the inner ply 88 are in an abutting or closely spaced relationship along a longitudinal line lying on the other side of the package center line near the other of the longitudinal joinder lines .96 and 98. Again, all of the features, advantages and alternatives that have heretofore been discussed earlier in connection with other embodiments are equally applicable.

Although the thicknesses of the plastic plies will usually be the same, one ply may be thickner than the other in order to achieve particular package characteristics. For example, superior strength may be imparted to the outer ply by making it somewhat thicker than the inner ply.FIG. 2C shows an example of such a package. It is similar in all respects to the package whose transverse section is shown in FIG. 28 except that the outer ply 1 10 is of a heavier gauge or thickness than the inner ply 112 to obtain certain advantagesand benefits as already discussed. It should be noted that when the thicknesses of the inner and outer plies are different, in

order to obtain transverse sections of uniform thick.

ness, the overlap is preferably obtained by overlapping portions of the outer ply only or the inner ply only as shown, for example, in FIGS. 2 and 2A.

In FIG. 4, an alternative configuration of the package of the invention is shown which has already been alluded to. In this embodiment, the overlapping configuration within the access opening is the same as that shownin FIG. 2 the only distinction being that the access opening and closure membrane (here referenced by the numeral 116) have been displaced substantially to one side of the longitudinal center line 118. Such package is most often and most conveniently used in the orientation shown in which the closure membrane 116 is adjacent the upper part of the package.

Although there have been described above a number of alternative forms and modifications of packages in accordance with the invention, it will be appreciated that the invention encompasses all modifications and variations falling within the scope of the appended claims. Thus, many other variations of the overlap scheme will become apparent to those with ordinary skill in the art. For example, in FIG. 2B, the overlapping portion 86 of the outer ply 84 could be positioned below the overlapping portion 90 of the inner ply 88.

What is claimed is:

l. A package for storing articles in substantially bacteria-free condition, comprising:

a flexible, plastic bag having a double wall and opposed ends and an access opening through said double wall, portions of said double wall overlapping with the confines of said access opening, substantially all cross-sections of said bag having substantially the same, uniform thickness, said double wall having a thickness at least sufficient to render said container essentially completely impermeable to bacteria; and,

a closure membrane covering said access opening and bonded to said bag about said access opening, said membrane being manually separable from said bag and essentially completely impermeable to bacteria but highly permeable to sterilizing vapor in comparison to said bag.

2. A package, as defined in claim 1, in which:

said double wall bag includes an inner ply and an outer ply, portions of said inner ply overlapping within the confines of said access opening.

3. A package, as defined in claim 1, in which:

said double wall bag includes an inner ply and an outer ply, portions of said outer ply overlapping within the confines of said access opening.

4. A package, as defined in claim 1, in which:

said double bag includes an inner ply and an outer ply, a portion of said inner ply overlapping with a portion of said outer ply within the confines of said access opening.

5. A package, as defined in claim 1, in which:

said double wall bag includes an inner ply and an outer ply having the same thickness.

6. A package, as defined in claim 1, in which:

said double wall bag includes an inner ply and an outer ply having difierent thicknesses.

7. A package, as defined in claim 1, in which:

said double wall bag is constructed of plastic capable of withstanding steam sterilization temperatures.

8. A package, as defined in claim 1, in which:

said double wall bag includes an inner ply and an outer ply, said plies being cohered to eliminate air between said plies.

9. A package for storing articles in bacteria-free condition, comprising:

a double wall plastic bag consisting of an inner ply and an outer ply, said plies having a combined thickness sufficient to render said bag essentially completely impermeable to bacteria, said plies having longitudinal edge portions and transverse edges, said transverse edges defining opposed ends of said bag, said plies being folded along longitudinal fold lines, one pair of said longitudinal edge portions disposed in spaced-apart relation to define a longitudinally-extending access opening, the other pair of said longitudinal edge portions being disposed in overlapping relation within the confines of said access opening, the combined thickness of said plies being substantially the same along substantially all portions of all transverse sections of said bag; and

a closure membrane covering said access opening,

said membrane being highly permeable to sterilizing vapor in comparison to said bag but essentially completely impermeable to bacteria, said membrane and said plies being bonded together by a longitudinal, continuous heat seal joinder line on each side of said access opening, said package includng a transverse, continuous heat seal joinder line adjacent one end of said package to unite said membrane and said plies and close said end of said package.

10. A package, as defined in claim 9, in which:

said overlapping longitudinal edge portions are portions of said outer ply.

11. A package, as defined in claim 9, in which:

said overlapping longitudinal edge portions are portions of said inner ply.

12. A package, as defined in claim 9, in which:

said overlapping longitudinal edge portions are portions of said inner and outer plies.

13. A package, as defined in claim 9, in which:

said plies are formed of material capable of withstanding steam sterilization temperatures and said membrane has adequate wet strength to withstand steam sterilization conditions.

14. A package, as defined in claim 9, in which:

the thickness of said inner ply is the same as the thickness of said outer ply.

15. A package, as defined in claim 9, in which:

the thickness of said inner ply is different than the thickness of said outer ply.

16. A package, as defined in claim 9, in which:

said clousre membrane has a tear strength greater than the strength of said longitudinal heat seal joinder lines so that said membrane is separable from said bag as a single piece so as to substantially completely expose said access opening.

17. A package, as defined in claim 9, in which:

said longitudinal heat seal joinder lines terminate a short distance from at least one of said ends of said package to define at least one pull tab on said closure membrane to facilitate its removal.

18. A package, as defined in claim 9, in which:

said closue membrane includes lateral gripping means adjacent at least one of said longitudinal heat seal joinder lines to facilitate removal of said membrane.

19. A package, as defined in claim 9, in which:

said plies are transparent and said closure membrane is in the form of a longitudinal strip substantially narrower than the overall width of the package to facilitate identification of the stored article.

20. A package as defined in claim 9, in which:

said package has a longitudinal center line and said access opening is substantially symmetrical of said center line.

21. A package, as defined in claim 9, in which:

said package has a longitudinal center line and said access opening is asymmetrical of said center line.

22. A package, as defined in claim 9, in which:

said plies are cohered to eliminate any air between i said plies.

23. A package for storing articles in bacteria-free condition, including:

a transparent, plastic bag essentially completely impermeable to bacteria and comprising longitudinally coextensive inner and outer plies of equal thickness, said plies having transverse edges defining opposed ends of said bag and longitudinal edge portions, said plies being folded along longitudinal fold lines to define opposed faces of the bag, one pair of said longitudinal edge portions disposed in parallel, spaced-apart relation to define a longitudinally-extending access opening, the other pair of said longitudinal edge portions being disposed in overlapping relation within the confines of said access opening, the combined thickness of said plies being substantially the same along substantially all portions of all transverse sections of said bag;

a longitudinallyextending, manually removable paper strip covering said access opening and extending the length of said bag, said strip being highly permeable to sterilizing vapor in comparison to said bag but essentially completely impermeable to bacteria, the overall width of said package being substantially greater than the width of said strip to make visible the contents of said package through either face therof, said strip and said plies being bonded together by a longitudinal, continuous heat seal joinder line on each side of said access opening, said strip havng a tear strength in relation to the strength of said longitudinal heat seal joinder lines sufficient so that said strip is separable from said bag in one piece; and, I

a transverse, continuous heat seal joinder line adjacent one end of said package uniting said strip and said plies and closing said end of said package.

24. A package, as defined in claim 23, in which:

said plies are formed of material capable of withstanding steam sterilization temperatures and said strip has adequate wet strength to withstand steam sterilization conditions.

25. A package, as defined in claim 23, in which:

said overlapping longitudinal edge portions includes an edge portion of said outer ply.

26. A package, as defined in claim 23, in which:

said overlapping longitudinal edge portions includes an edge portion of said inner ply.

27. A package, as defined in claim 23, in which:

said plies are cohered to eliminae air from between said plies.

28. A package, as defined in claim 27, in which:

said plies are cohered mechanically by embosisng said plies.

29. A package, as defined in claim 23, in which:

said longitudinal heat seal joinder lines terminate a short distance from at least one of said ends of said package to define at least one end tab on said paper strip to facilitate its removal.

UNITED STA'IES m'nm'r OFFICZ'C CERTIZ' XCATJJ OF C035 TIC-N Patent n 3 .761.013 w m se mmher425 ,1913.

Infientofl Samuel .T. Schus'rer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 25, for "sterizing" read "sterilizing"; Column 2 line 29 for "eithr" read --either--; line 60, for

"of" read --by-*. Column 3, line 39, for "sucy" read "such"; line 42 for "inveniton" read --invention--. Column 4, line 31, for "pverlapping" read --overlapping--; line 61, for "pair" read --air--. Column 5, line 64, for 'Fig." read --Figs Column 7, line 15 for "possibly" read "possible", line 26, 'for "Du Pont" read --du Pont-; line 37 for "temperautre" read "temperature"; line 58, for "memebrane" read 1 --membrane-. Column 8, line 7, for 'tIHasread -trans- 7 Column l0, line 48, for "thickner" read --thicker--; line 61, after "portions of the" insert --inner and outer plies rather than overlapping portions of the- Column 11, line 23, for "with" read --within--; line 27-, for "container" read --bag--; line 44, after "double" and before "bag" insert --wall--. Column 12 line 55 for "clo'sue" read --closure-- Column 13, line 32 for "therof" read --there of", Column 14, line 22 for "eliminae" read --eliminate--; line 25, for '"embosisng" read --embossing-.

Signed and sealed this 6th day of August 197M.

E Attest:

McCOY M. CIBSON, JR. I i C. MARSHALL DANN' Attesting Officer Commissioner ofPatents 

2. A package, as defined in claim 1, in which: said double wall bag includes an inner ply and an outer ply, portions of said inner ply overlapping within the confines of said access opening.
 3. A package, as defined in claim 1, in which: said double wall bag includes an inner ply and an outer ply, portions of said outer ply overlapping within the confines of said access opening.
 4. A package, as defined in claim 1, in which: said double bag includes an inner ply and an outer ply, a portion of said inner ply overlapping with a portion of said outer ply within the confines of said access opening.
 5. A package, as defined in claim 1, in which: said double wall bag includes an inner ply and an outer ply having the same thickness.
 6. A package, as defined in claim 1, in which: said double wall bag includes an inner ply and an outer ply having different thicknesses.
 7. A package, as defined in claim 1, in which: said double wall bag is constructed of plastic capable of withstanding steam sterilization temperatures.
 8. A package, as defined in claim 1, in which: said double wall bag includes an inner ply and an outer ply, said plies being cohered to eliminate air between said plies.
 9. A package for storing articles in bacteria-free condition, comprising: a double wall plastic bag consisting of an inner ply and an outer ply, said plies having a combined thickness sufficient to render said bag essentially completely impermeable to bacteria, said plies having longitudinal edge portions and transverse edges, said transverse edges defining opposed ends of said bag, said plies being folded along longitudinal fold lines, one pair of said longitudinal edge portions disposed in spaced-apart relation to define a longitudinally-extending access opening, the other Pair of said longitudinal edge portions being disposed in overlapping relation within the confines of said access opening, the combined thickness of said plies being substantially the same along substantially all portions of all transverse sections of said bag; and a closure membrane covering said access opening, said membrane being highly permeable to sterilizing vapor in comparison to said bag but essentially completely impermeable to bacteria, said membrane and said plies being bonded together by a longitudinal, continuous heat seal joinder line on each side of said access opening, said package includng a transverse, continuous heat seal joinder line adjacent one end of said package to unite said membrane and said plies and close said end of said package.
 10. A package, as defined in claim 9, in which: said overlapping longitudinal edge portions are portions of said outer ply.
 11. A package, as defined in claim 9, in which: said overlapping longitudinal edge portions are portions of said inner ply.
 12. A package, as defined in claim 9, in which: said overlapping longitudinal edge portions are portions of said inner and outer plies.
 13. A package, as defined in claim 9, in which: said plies are formed of material capable of withstanding steam sterilization temperatures and said membrane has adequate wet strength to withstand steam sterilization conditions.
 14. A package, as defined in claim 9, in which: the thickness of said inner ply is the same as the thickness of said outer ply.
 15. A package, as defined in claim 9, in which: the thickness of said inner ply is different than the thickness of said outer ply.
 16. A package, as defined in claim 9, in which: said clousre membrane has a tear strength greater than the strength of said longitudinal heat seal joinder lines so that said membrane is separable from said bag as a single piece so as to substantially completely expose said access opening.
 17. A package, as defined in claim 9, in which: said longitudinal heat seal joinder lines terminate a short distance from at least one of said ends of said package to define at least one pull tab on said closure membrane to facilitate its removal.
 18. A package, as defined in claim 9, in which: said closue membrane includes lateral gripping means adjacent at least one of said longitudinal heat seal joinder lines to facilitate removal of said membrane.
 19. A package, as defined in claim 9, in which: said plies are transparent and said closure membrane is in the form of a longitudinal strip substantially narrower than the overall width of the package to facilitate identification of the stored article.
 20. A package as defined in claim 9, in which: said package has a longitudinal center line and said access opening is substantially symmetrical of said center line.
 21. A package, as defined in claim 9, in which: said package has a longitudinal center line and said access opening is asymmetrical of said center line.
 22. A package, as defined in claim 9, in which: said plies are cohered to eliminate any air between said plies.
 23. A package for storing articles in bacteria-free condition, including: a transparent, plastic bag essentially completely impermeable to bacteria and comprising longitudinally coextensive inner and outer plies of equal thickness, said plies having transverse edges defining opposed ends of said bag and longitudinal edge portions, said plies being folded along longitudinal fold lines to define opposed faces of the bag, one pair of said longitudinal edge portions disposed in parallel, spaced-apart relation to define a longitudinally-extending access opening, the other pair of said longitudinal edge portions being disposed in overlapping relation within the confines of said access opening, the combined thickness of said plies being substantially the same along substantially all portions of all transverse sections of said bag; a longitudinally-extenDing, manually removable paper strip covering said access opening and extending the length of said bag, said strip being highly permeable to sterilizing vapor in comparison to said bag but essentially completely impermeable to bacteria, the overall width of said package being substantially greater than the width of said strip to make visible the contents of said package through either face therof, said strip and said plies being bonded together by a longitudinal, continuous heat seal joinder line on each side of said access opening, said strip havng a tear strength in relation to the strength of said longitudinal heat seal joinder lines sufficient so that said strip is separable from said bag in one piece; and, a transverse, continuous heat seal joinder line adjacent one end of said package uniting said strip and said plies and closing said end of said package.
 24. A package, as defined in claim 23, in which: said plies are formed of material capable of withstanding steam sterilization temperatures and said strip has adequate wet strength to withstand steam sterilization conditions.
 25. A package, as defined in claim 23, in which: said overlapping longitudinal edge portions includes an edge portion of said outer ply.
 26. A package, as defined in claim 23, in which: said overlapping longitudinal edge portions includes an edge portion of said inner ply.
 27. A package, as defined in claim 23, in which: said plies are cohered to eliminae air from between said plies.
 28. A package, as defined in claim 27, in which: said plies are cohered mechanically by embosisng said plies.
 29. A package, as defined in claim 23, in which: said longitudinal heat seal joinder lines terminate a short distance from at least one of said ends of said package to define at least one end tab on said paper strip to facilitate its removal. 